Duct system inspection

HVAC DUCT SYSTEMS INSPECTION GUIDESECOND EDITION — JUNE 2000 SHEET METAL AND AIR CONDITIONING CONTRACTORS’ NATIONAL ASSOCIATION, INC... HVAC DUCT SYSTEMS INSPECTION GUIDECOPYRIGHT E 2000

HVAC DUCT SYSTEMS INSPECTION GUIDE

SHEET METAL AND AIR CONDITIONING CONTRACTORS’

NATIONAL ASSOCIATION, INC.

HVAC DUCT SYSTEMS INSPECTION GUIDE

SECOND EDITION — JUNE 2000

SHEET METAL AND AIR CONDITIONING CONTRACTORS’

NATIONAL ASSOCIATION, INC.

4201 Lafayette Center Drive Chantilly, VA 20151 1209

HVAC DUCT SYSTEMS INSPECTION GUIDE

COPYRIGHT E 2000 All Rights Reserved

by

SHEET METAL AND AIR CONDITIONING CONTRACTORS’

NATIONAL ASSOCIATION, INC.

4201 Lafayette Center DriveChantilly, VA 20151 1209

Printed in the U.S.A.

FIRST EDITION 1989SECOND EDITION JUNE 2000

Except as allowed in the Notice to Users and in certain licensing contracts, no part of this book may bereproduced, stored in a retrievable system, or transmitted, in any form or by any means, electronic,mechanical, photocopying, recording, or otherwise, without the prior written permission of the publisher

iii HVAC Duct Systems Inspection GuideSecond Edition

FOREWORD

One definition of inspect is “to view closely and critically.” In building construction the term “inspection” brings tomind many other terms: completeness, compliance, conformance, quality assurance, design deficiency, oversight, ne-glect, unauthorized substitution, defects and omissions, punch list, responsible party, call back, and payment retention

In any case the mechanical systems inspector plays an important role in contract compliance or code compliance fication Knowledge and reasonableness are prerequisites for employment in this capacity This guide is based on theassumption that SMACNA duct construction standards and installation recommendations are linked to contract orcode compliance It is an administrative guide to the inspection of duct systems It can serve as a study guide for thoseneeding an introduction to the functions of duct systems, to the nature of ductwork, and to the SMACNA documents

veri-it previews Study of the complete texts of the excerpted edveri-itions is necessary and encouraged Familiarveri-ity wveri-ith all

of the documents that regulate duct system installation will enable inspectors to develop their own checklists and toestablish scales of importance that are consistent with their duties

NOTE: The provisions herein are not intended to constitute contract requirements in and of themselves The SMACNA manuals to which this guide refer contain many alternative constructions They also contain many details that are obligatory Other details are left to the prudent judgement of the contractor Thus, this document is no substitute for familiarity with all of the provisions in the other manuals.

The following SMACNA manuals are excerpted within this guide:

SHVAC Duct Construction Standards, Second Edition, 1995

SFibrous Glass Duct Construction Standards, Sixth Edition, 1992

SFire, Smoke, and Radiation Damper Installation Guide for HVAC Systems, Fourth Edition, 1992

SHEET METAL AND AIR CONDITIONING CONTRACTORS’

NATIONAL ASSOCIATION, INC

FORMER TASK FORCE MEMBERS AND OTHER CONTRIBUTORS

Donald Cunningham, Chairman

John H StrattonChantilly, VA

Eli HowardChantilly, VA

c) By using the data contained in the product user accepts the Data “AS IS” and assumes all risk of loss, harm or injury that may result from its use User acknowledges that the Data is complex, subject to faults and requires verification by competent professionals, and that modification of parts of the Data by user may impact the results or other parts of the Data.

d) IN NO EVENT SHALL SMACNA BE LIABLE TO USER, OR ANY OTHER PERSON, FOR ANY INDIRECT, SPECIAL OR CONSEQUENTIAL DAMAGES ARISING, DIRECTLY OR INDIRECTLY, OUT OF OR RELATED TO USER’S USE OF SMACNA’S PRODUCT OR MODIFICATION OF DATA THEREIN This limitation of liability applies even if SMACNA has been advised of the possibility of such damages IN NO EVENT SHALL SMACNA’S LIABILITY EXCEED THE AMOUNT PAID BY USER FOR ACCESS TO SMACNA’S PRODUCT OR $1,000.00, WHICHEVER IS GREATER, REGARDLESS OF LEGAL THEORY.

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a) A formal interpretation of the literal text herein or the intent of the technical committee or task force associated with the document

or publication is obtainable only on the basis of written petition, addressed to the Technical Resources Department and sent to the Association’s national office in Chantilly, Virginia In the event that the petitioner has a substantive disagreement with the interpretation,

an appeal may be filed with the Technical Resources Committee, which has technical oversight responsibility The request must pertain

to a specifically identified portion of the document that does not involve published text which provides the requested information In considering such requests, the Association will not review or judge products or components as being in compliance with the document

or publication Oral and written interpretations otherwise obtained from anyone affiliated with the Association are unofficial This procedure does not prevent any committee or task force chairman, member of the committee or task force, or staff liaison from expressing

an opinion on a provision within the document, provided that such person clearly states that the opinion is personal and does not represent an official act of the Association in any way, and it should not be relied on as such The Board of Directors of SMACNA shall have final authority for interpretation of this standard with such rules or procedures as they may adopt for processing same b) SMACNA disclaims any liability for any personal injury, property damage, or other damage of any nature whatsoever, whether special, indirect, consequential or compensatory, direct or indirectly resulting from the publication, use of, or reliance upon this document SMACNA makes no guaranty or warranty as to the accuracy or completeness of any information published herein.

b) In issuing and making this document available, SMACNA is not undertaking to render professional or other services for or on behalf

of any person or entity SMACNA is not undertaking to perform any duty owed to any person or entity to someone else Any person

or organization using this document should rely on his, her or its own judgement or, as appropriate, seek the advice of a competent professional in determining the exercise of reasonable care in any given circumstance.

7 REPRINT PERMISSION

Non-exclusive, royalty-free permission is granted to government and private sector specifying authorities to reproduce only any

construction details found herein in their specifications and contract drawings prepared for receipt of bids on new construction and renovation work within the United States and its territories, provided that the material copied is unaltered in substance and that the reproducer assumes all liability for the specific application, including errors in reproduction.

8 THE SMACNA LOGO

The SMACNA logo is registered as a membership identification mark The Association prescribes acceptable use of the logo and expressly forbids the use of it to represent anything other than possession of membership Possession of membership and use of the logo

in no way constitutes or reflects SMACNA approval of any product, method, or component Furthermore, compliance of any such item with standards published or recognized by SMACNA is not indicated by presence of the logo.

TABLE OF CONTENTS

TABLE OF CONTENTS

FOREWORD iii

FORMER TASK FORCE MEMBERS AND OTHER CONTRIBUTORS iv

NOTICE TO USERS OF THIS PUBLICATION v

TABLE OF CONTENTS vii

CHAPTER 1 SCOPE 1.1

1.1 SCOPE .1.1 1.2 WHAT IS THE PURPOSE OF INSPECTION? 1.1 1.3 WHAT IS THE VALUE OF INSPECTION? .1.1 1.4 WHAT IS THE COST OF INSPECTION? 1.1 1.5 DOES THE TIMING OF INSPECTIONS AFFECT CONSTRUCTION COSTS? .1.1 1.6 WHAT RISKS ARE INVOLVED WHEN INSPECTIONS ARE NOT DONE OR ARE

NOT DONE PROPERLY? .1.1 1.7 WHAT QUALIFICATIONS ARE NEEDED BY INSPECTORS? 1.2 1.8 HOW DO I USE THIS GUIDE? 1.2 1.9 DUCT INSPECTIONS OVERVIEW .1.2

CHAPTER 2 COMPLIANCE AND QUALITY CONTROL 2.1

2.1 COMPLIANCE AND QUALITY CONTROL 2.1 2.2 CHECKLISTS 2.1

APPENDIX A FUNCTIONS OF DUCTED AIR HANDLING SYSTEMS A.1

A.1 VENTILATION AND AIR CONDITIONING A.1 A.2 CENTRAL AIR HANDLING SYSTEM A.1 A.3 DEDICATED EXHAUST SYSTEMS A.1 A.4 ROOM AIR DISTRIBUTION A.1 A.5 ROOM PRESSURE CONTROL A.2 A.6 INFILTRATION AND EXFILTRATION A.2 A.7 CENTRAL ALARM CONTROL STATIONS A.2 A.8 TESTING AND BALANCING A.2 A.9 SYMBOLS A.2

APPENDIX B DUCT CONSTRUCTION MATERIALS B.1

B.1 GALVANIZED STEEL B.1 B.2 CARBON STEEL (BLACK IRON) B.1 B.3 STAINLESS STEEL B.1 B.4 ALUMINUM B.1 B.5 COPPER B.1 B.6 FIBERGLASS REINFORCED PLASTIC (FRP) B.1 B.7 POLYVINYL CHLORIDE (PVC) B.2 B.8 POLYVINYL STEEL (PVS) B.2 B.9 CONCRETE B.2 B.10 ASBESTOS CEMENT B.2 B.11 RIGID FIBROUS GLASS B.2 B.12 GYPSUM BOARD B.2

APPENDIX C HVAC DUCT CONSTRUCTION STANDARDS C.1

C.1 DUCT CONSTRUCTION AND INSTALLATION STANDARDS C.1

viii HVAC Duct Systems Inspection GuideSecond Edition

C.2 DUCT SEALING COMMENTARY C.3C.3 RECTANGULAR DUCT REINFORCEMENT C.5C.4 INTRODUCTION TO THE RECTANGULAR DUCT CONSTRUCTION

SCHEDULES C.8C.5 TRANSVERSE JOINTS FOR RECTANGULAR DUCT C.25C.6 VOLUME DAMPERS (NOTES FOR FIGURES C 16 AND C 17) C.41C.7 COMMENTARY C.41C.8 SPECIFICATION FOR SUPPORTING FLEXIBLE DUCT C.47C.9 ROUND DUCT CONSTRUCTION STANDARDS C.50C.10 COMMENTARY C.50C.11 CASING AND PLENUM CONSTRUCTION STANDARDS C.69

APPENDIX D FIRE, SMOKE, AND RADIATION DAMPER GUIDE D.1

APPENDIX E FIBROUS GLASS DUCT CONSTRUCTION E.1

E.1 FIBROUS GLASS DUCT CHARACTERISTICS AND LIMITATIONS E.1E.2 CLOSURES E.2E.3 ADDITIONAL FIBROUS GLASS DUCT CONSTRUCTION DETAILS E.5

B 1 Galvanized Sheet Thickness Tolerances B.3B 2 Manufacturers Standard Gage-Thickness (Uncoated Steel) B.4B 3 Stainless Steel Sheet Thickness B.5B 4 Aluminum Sheet Thickness (Alloy 3003 H14)) B.6C 1 Standard Duct Sealing Requirements C.2C 2 Rectangular Duct Reinforcement C.14C 2M Rectangular Duct Reinforcement C.15C 3 Unreinforced Duct (Wall Thickness) C.18C 3M Unreinforced Duct (Wall Thickness) C.19C 4 Intermediate Reinforcement C.28C 4M Intermediate Reinforcement C.29C 5 Transverse Joint Reinforcement C.30C 5M Transverse Joint Reinforcement C.31C 6 Transverse Joint Reinforcement C.32C 6M Transverse Joint Reinforcement C.33C 7 Mitered Elbows C.51C 8 Round Duct Gage Unreinforced Positive Pressure C.52C 8M Round Duct Gage Unreinforced Positive Pressure C.53C 9 Rectangular Duct Hangers Minimum Size C.60C 9M Rectangular Duct Hangers Minimum Size C.61C 10 Minimum Hanger Sizes for Round Duct C.62D 1 Recommended Fire Damper Installation Instructions D.1D 2 Recommended Minimum Sleeve Thickness for Fire Dampers D.3E 1 Tie Rod System Reinforcement Schedule E.8E 1M Tie Rod System Reinforcement Schedule E.9E 2 Channel System Reinforcement Schedule E.12E 2M Channel System Reinforcement Schedule E.13E 3 Partial Wrap around Reinforcement Schedule E.16E 3M Partial Wrap around Reinforcement Schedule E.17E 4 Maximum Hanger Spacing by Duct Size, I.D E.19E 5 Channel Selection E.19

FIGURES

A 1 Symbols for HVAC Systems A.4A 1M Symbols for HVAC Systems (Metric) A.5A 2 Single Duct System A.6A 3 Terminal Reheat System A.6A 4 Multi zone System A.7A 5 Variable Volume System A.7A 6 Duct System Example A.8A 6M Duct System Example (Metric) A.9A 7 Duct Pressure Class Designation A.10C 1 Dependent Variables C.7C 2 Reading Guide Summary C.9C 3 Unreinforced Duct C.16C 4 Crossbroken and Beaded Duct C.20C 5 Flexible Duct Liner Installation C.21C 6 Liner Fasteners C.22C 7 Duct Reinforced on Two Sides C.23C 8 Reinforcement Attachment C.24C 9 Transverse (Girth) Joints C.26C 10 Special Joint Profiles C.34C 11 Longitudinal Seams Rectangular Duct C.35C 12 Rectangular Elbows C.36C 12 Rectangular Elbows (Continued) C.37C 13 Vanes and Vane Runners C.38C 14 Vane Support in Elbows C.39C 15 Branch Connections C.40

x HVAC Duct Systems Inspection GuideSecond Edition

C 16 Volume Dampers Single Blade Type C.42C 17 Multiblade Volume Dampers C.43C 18 Offsets and Transitions C.44C 19 Remote Heating and Cooling Coil Installations C.45C 20 Ceiling Diffuser Branch Ducts C.46C 21 Flexible Duct Supports C.48C 22 Flexible Duct Supports C.49C 23 Seams Round Duct and Fittings C.54C 24 Transverse Joints Round Duct C.55C 25 Hanger Attachments to Structures C.56C 26 Upper Attachment Devices Typical C.57C 27 Lower Hanger Attachments C.58C 28 Riser Supports From Floor C.64C 28M Riser Supports From Floor C.65C 29 Rooftop Duct Installation C.66C 30 Equipment and Duct Support Flashing C.67C 31 Rectangular Gooseneck C.68C 32 Built up Standing Seam Casing C.70C 33 Dishwasher Vapor Exhaust C.71D 1 Basic Fire Damper Installation Details D.2D 2 UL Duct sleeve Connections (Breakaway Connections) D.4D 2 UL Duct sleeve Connections (Breakaway Connections) (Continued) D.5D 3 Fire Damper Opening Protection D.6D 4 Curtain Fire Dampers D.7D 5 Combination Fire and Smoke Dampers D.8D 6 Duct Liner Interruption D.9D 7 Access Doors and Panels D.10D 8 Leakage Rated (Smoke) Damper D.11D 9 Fire Rated Ceiling Assemblies D.12E 1 Tape Closure Joint, with Staple Flap E.3E 2 Tape Closure Joint, without Staple Flap E.3E 3 Closures (Continued) E.4E 4 Tie Rod Reinforcement At Joint E.5E 5 Sheet Metal and Equipment Connection Details E.6E 6 Sheet Metal and Equipment Connection Details (Continued) E.7E 7 Tie Rod Reinforcement E.8E 7M Tie Rod Reinforcement E.9E 8 Tie Rod Termination Methods E.10E 9 Channel Reinforcement, Positive Pressure Systems E.14E 10 Channel Reinforcement, Negative Pressure Systems E.15E 11 Partial Wrap around Reinforcement E.16E 11M Partial Wrap around Reinforcement E.17E 12 Allowable Hanger Spacing, Straight Duct – 3 Inch Wide Channels E.18E 13 Hanger Spacing and Extension – 3 Inch Wide Channels E.19E 14 Use of 2 Inch Wide Hanger Channels E.19E 15 Access Door, Flange on Opening E.20

CHAPTER 1

INTRODUCTION

SCOPE CHAPTER 1

1.1 HVAC Duct Systems Inspection GuideSecond Edition

This document gives reasons for doing inspections of

air handling systems, provides outlines that can be

used to organize and conduct inspections, and sets

forth checklists that call attention to the basic features

of ductwork and items placed in duct systems

It presumes that SMACNA’s construction standards

are used as the basis of compliance, whether they are

explicitly invoked in contract documents or in codes

No attempt is made to segregate designer’s inspection

obligations from those of code officials

It is primarily prepared for commercial HVAC

sys-tems; however, similar principles would apply for

resi-dential or industrial work inspection Furthermore, it

assumes that prescription specifications apply rather

than performance specifications Performance

specifi-cations typically call for HVAC systems to maintain

control of the environmental within certain tolerances

Whether the duct system has the specified airflow rate,

maintains air temperature, humidity, degree of

cleanli-ness, etc., or whether it controls room air motion and

pressure differentials in relation to adjacent spaces are

separate matters of design and testing and balancing

that are already dealt with in numerous handbooks and

standards An overview of the functions of duct

sys-tems is given in Appendix A

Finally, although this document covers some items

that are safety related, this document is not a safety

in-spection guide It is presumed that the applicable

codes and system designs that are allowing use of the

SMACNA standards and manuals address safety

is-sues independently

1.2 WHAT IS THE PURPOSE OF

INSPECTION?

The purpose of inspection is to determine if the

construction and installation comply with the

docu-ments for which the inspector is responsible

1.3 WHAT IS THE VALUE OF

INSPECTION?

The value of inspection is the assurance that the

mate-rials and assemblies purchased are either provided and

available or that defects and omissions are

man-1.5 DOES THE TIMING OF

INSPECTIONS AFFECT CONSTRUCTION COSTS?

The timing of inspections has a definitive impact onconstruction costs The work that will be concealed orinaccessible for inspection after installation should beinspected while work is in progress Delay in construc-tion progress may occur if further work has to be sus-pended pending inspection Correcting deficienciesafter installations are complete is expensive and timeconsuming; it may affect the work of several trades; itmay result in delays in payment or in contract close-out; it can even result in delayed occupancy or delayeduse of the facilities

1.6 WHAT RISKS ARE INVOLVED

WHEN INSPECTIONS ARE NOT DONE OR ARE NOT DONE PROPERLY?

Some of the risks involved when inspections are notdone or not done properly are:

a Less qualified or less scrupulous contractorswill gamble that omissions and defects will

go undetected and will under-price the work

or make excessive profits

b Owner dissatisfaction will lead to litigation

c Occupant dissatisfaction with indoor airquality and safety can result

d Disruptive delays in occupancy and use canoccur

e Expensive corrective work at a later date will

be required

f Hazards that should be detected are not

g The inspector’s employer will have liabilityfor consequences of delay and damage or loss

h Adverse publicity can disrupt normal ness practices

busi-i Bonding companies may have to completethe project

j Different insurance will be needed than was

1.8 HOW DO I USE THIS GUIDE?

This guide is intended to acquaint inspection officials,

designers, and contractors with the basic features of

duct construction, equipment connections to ducts and

items inserted in ducts as they are found in the

SMACNA manuals

NOTE: The provisions herein are not intended to

constitute contract requirements in and of themselves.

The SMACNA manuals to which this guide refer

con-tain many alternative constructions They also concon-tain

many details that are obligatory Other details are left

to the prudent judgement of the contractor Thus, this

document is no substitute for familiarity with all of the

provisions in the other manuals.

The following SMACNA manuals are excerpted within

SFire, Smoke, and Radiation Damper Installation

Guide for HVAC Systems, Fourth Edition, 1992

However, this guide does provide a framework of

knowledge and perspective that should provide a

“feel” for construction that complies with SMACNA

standards When something is found on a job site that

doesn’t “look like” what is described herein, the

in-spector should examine a specific submittal, shop

drawing, coordinated drawing, standard, or code to

as-certain whether the installation is or is not in

com-pliance Otherwise, the checklists are useful in

survey-ing the contract documents to find the subjects that are

actually in a specific project Edited versions of them

can be created in the office environment so that they,

along with any necessary documents, can be taken to

a construction site to perform inspections

Inspection plays a vital role in contract complianceand it assures that quality and performance are consis-tent with the design It has recognizable dollar valuethat owners and citizens can recognize and appreciate

1.9 DUCT INSPECTIONS OVERVIEW

Some guidelines for a duct inspection are presentedbelow:

a Prerequisites for conducting inspections:

1 Possess general knowledge of the

crafts-manship of ducts

2 As applicable, conduct thorough

ex-amination of contract plans, tions, change orders, submittals, code re- quirements, and standards invoked by

specifica-these documents

3 Identify framing requirements and fire stopping for ducted penetrations of building structures and review clear- ances to combustible materials

4 Prepare lists of items to be inspected

5 Anticipate work progress schedules,

par-ticularly for ductwork that will be cessible after concealment or invisibleafter insulation is applied

inac-6 Clarify authority to approve, inspect,

re-ject, and suspend work and to withholdoccupancy permits

b Arrange a meeting when possible betweenInspector(s) and Job Supervisors prior to be-ginning installation to review the completerequirements for ductwork

1 Materials

Review requirements

2 Duct Construction Schedules

Review wall thickness, reinforcements,joints and seams, and pressure classifica-tion as applicable to each system

3 Duct System Supports

Review support methods for ducts andapparatus to which they connect

4 Flexible Duct/Connector

Review length, type, configuration, port, and requirements for listing and la-belling of flexible ducts and flexibleconnectors

sup-5 Sealants

Review types and required use of

seal-1.3 HVAC Duct Systems Inspection GuideSecond Edition

ants, as needed, for ducts, fittings,

con-nections, and casing

6 Barrier Penetrations

Review methods of penetrating fire and

smoke barriers

7 Access

Review maintenance access

require-ments and size and location of access

doors

8 Air Terminals

Review provisions for locating and

sup-porting grilles, diffusers, and registers

9 Volume Control Devices

Examine methods of automatic or

manu-al bmanu-alancing of airflow in systems

10 Building Compartment Leakage

Investigate the airtightness of building

compartments to be pressurized under

emergency mode situations

11 Plenums

Review construction of field erected

ple-nums and casings and clearances for

maintenance and operation within these

12 Special Duty Systems

Give due attention to special duty

sys-tems such as grease hood and fume hood

exhausts, dishwasher and shower room

exhausts, engineered smoke control

Determine what tests are required, any

concealment contingencies, what

re-ports are to be filed, and what

witness-ing, if any, is required

c Conduct appropriate periodic inspections

us-ing checklists

1 Visually inspect the installation

2 Witness qualification and operating tests

as required

3 Look for labels and imprintings that are

required for factory-made products

d Give contractors appropriate and timely tice of deficiencies and omissions

no-e Special Notices:

1 The designer of an air system is required

to show the locations and mounting rangement of all fire dampers, smoke

ar-dampers, through-penetration firestops,

and similar protection means on the tract drawings This is usually required

con-in codes as a prerequisite for tion permit issuance Likewise, he is re-quired to show on the contract drawingsall air volume regulating devices re-quired to balance the system SMACNAstrongly endorses a contractor’s right to

construc-an equitable contract adjustment for allsuch devices not shown on the contractdrawings

2 The use of gypsum wallboard as ductmaterial is relatively rare Constructionstandards for such use, except as airshafts, do not exist Temperature, humid-ity, leakage, and damage susceptibilityare all factors that limit its use in applica-tions other than ceiling plenums and airshafts Limitations in the specific codeshould be checked

3 The duct may be only designated to be

“reasonably airtight.” This terminology

is commonly found in mechanical codesand in fire protection related standardssuch as NFPA 90A Since it has no quan-titative evaluation criteria it means thatwhatever leakage results from using theprescribed duct construction methodsand good workmanship is acceptable.Good workmanship would be that per-ceived to be such in the trade

SMACNA manuals do not set allowable leakage rates or require leakage tests It

is the system designer’s duty to prescribethese if needed Comprehensive analysis

of leakage, leakage rates expected insealed and unsealed ducts, leakage clas-sifications, and test procedures are in the

SMACNA HVAC Air Duct Leakage Test Manual SMACNA does not designate

specific methods of sealing

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CHAPTER 2

COMPLIANCE AND QUALITY CONTROL

COMPLIANCE AND QUALITY CONTROL CHAPTER 2

2.1 COMPLIANCE AND QUALITY

CONTROL

Although knowledge of the details in the construction

standards is the ultimate basis of quality control,

installations should also be checked by routinely

look-ing for the presence or absence of general features that

reflect the level of quality

2.2 CHECKLISTS

The following checklists provide information andcompliance and quality control Not all projects willhave all items listed in the checklist

2.2 HVAC Duct Systems Inspection GuideSecond Edition

SPECIAL CONDITIONS REVIEW CHECKLIST

Duct pressure classes are clearly given on the drawings or in the specifications for each system

The amount of sealing is specified or an allowable leakage rate is given

Field tests other than testing and balancing are required

The configuration of duct fittings is specified It is determined by:

design documents

clarification by submittals

contractor’s choice of options in the SMACNA manuals

As-built ductwork deviates from the design documents It was influenced by:

The project requires seismic restraints on mechanical systems

Ductwork is not supporting items that are not of the sheet metal trade

Air passageways in return air ceilings and in shafts are not blocked

There is sufficient space in and behind access doors or panels in ceilings, walls, and shafts to allow a

person to perform maintenance on the HVAC system devices that require it

Maintenance access in ducts is provided Its form is:

hinged panels

lift off panels

removable sections of ducts

Automatic monitoring devices to be mounted in or on ducts are present and operable:

fire stats

freeze stats

smoke detectors

fail-safe air flow switches

damper position indicators

Early occupancy and warranty period adjustments

Owner’s operating and maintenance instructions:

by designers

by contractors

DUCT SYSTEM INSPECTION CHECKLIST

RIGID DUCTWORK

Trunk-Branch Fitting
In Slab

Weatherproofing

Through-penetration Firestop

Duct Grade/Class
Ceiling Plenum Contents

2.4 HVAC Duct Systems Inspection GuideSecond Edition

INSPECTION CHECKLIST FOR FIBROUS GLASS DUCT SYSTEM INSTALLATION

References

SMACNA Standards

North American Installation Manufacturers Association (NAIMA)

Board Manufacturer’s Standards

2 Is system operating within the design limitations for which it was built?

6 Is the system free from visual signs of duct board facing delamination?

Fabrication and Installation

7 Are turning vanes installed in accordance with the Standards? (Pressing your hand into the

cheek of the ell will reveal if specified vanes are being used.)

8 When metal parts are attached, are 21_w in (63.5 mm) (minimum) square steel washers used

on 16 in (405 mm) (maximum) centers?

9 When staples can’t be used, are 8 in (203 mm) cross tabs of approved closure being used in

place of staples? (Tab spacing requirements are 12 in (305 mm) OC, minimum one per side)

10 Is the system completely free from tears or punctures in the facing?

11 Is the system free from areas where excessive amounts of closure materials, such as

several wraps around a joint, may have been used to conceal potential problem areas?

12 Are all system joints tight, free from bulges, with taped joints showing good workmanship?

13 Are all fittings fabricated in accordance with the Standards and do they demonstrate good

workmanship?

14 Have offsets been installed so duct sections aren’t forced to bend around obstructions?

15 Are all panels in any fitting at least 4 in (102 mm) long, including male or female joints?

Electric Heaters

16 Is interior sleeve present, properly attached with screws and washers 16 in (405 mm) on

centers?

18 Are all listed clearances to combustibles and radiation protections in place?

22 Is duct properly attached to sleeve with screws and washers 16 in (405 mm) on centers

and sealed?

Access Doors

Grilles, Diffusers, Registers

24 Is the extra weight of the item being separately supported and not dependent on the duct

alone for support?

(EXCEPTION: Registers not greater than 150 in2(0.097 m2) in area may be attached to the duct with metalchannel without other support.)

Equipment Unit Connection Yes No

25 Are sheet metal screws and washers used to secure duct system to flange extensions?

(Mechanical fasteners must be used!)

Closure

27 Are closure materials of a listed type as evidenced by presence of UL instruction sheet in

duct board carton? Is tape imprinted?

28 Are there staples or cross tabs, properly spaced, on circumferential joints?

29 Are staples, if used, of the correct type and size, and spaced in proper intervals as

recommended by the duct board manufacturer?

30 Are all pressure-sensitive tape closures rubbed down adequately, with staples or scrim in

facing clearly visible through the tape?

31 If heat-sealable tape closure was used, was it applied correctly, as evidenced by dot color

change?

32 If glass fabric and mastic are used, is the mesh of the glass fabric completely filled with

mastic?

Reinforcement

33 Is reinforcement system of recommended type (formed metal, tie rod, or combination)?

35 Is tie rod spacing correct according to duct span, board type, and static pressure?

36 Are tie rod washers 21_w in (63.5 mm) square and proper gage by type?

37 Do tie rod washers have turned edges facing away from duct board so they won’t cut into it?

38 If tie rods reinforce a butt joint, are rods used on both sides of butt joint?

40 Are anti-sag devices used on ducts 48 in (1220 mm) span or greater, to support top panel of

ducts?

42 Are heels of tees, elbows, and end caps reinforced (formed sheet metal channel, tie rod, or

combination)?

43 When formed sheet metal channel reinforcement is used, are sheet metal gages, dimensions,

and spacing correct?

44 On supply ducts, is reinforcing member on the female side of the shiplap?

45 On return ducts, are sheet metal channel reinforcements attached to ducts with screws and

21_w in (63.5 mm) square washers or 2 × 6 in (51 × 150 mm) clips?

46 On return ducts, is the reinforcing member attached to the male shiplap side of the joint?

47 For the heels of tees, elbows, end caps, and any other fittings where a panel faces an opening

on the opposite side, is correct reinforcing member (type: sheet metal channel, tie rod, or

combination) applied?

Hangers and Supports

50 Are accessories that add weight to the duct system separately supported so as not to stress

the system? (consult the standards)

51 Are vertical risers limited to two stories and supported on 12 ft (3650 mm) (maximum)

centers?

52 If formed sheet metal reinforcements are used as hangers, are attachments within 6 in

(150 mm) of duct sides?

53 Are all fittings supported by hangers in accordance with the standards?

2.6 HVAC Duct Systems Inspection GuideSecond Edition

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APPENDIX A

FUNCTIONS OF DUCTED AIR HANDLING SYSTEMS

FUNCTIONS OF DUCTED AIR HANDLING SYSTEMS APPENDIX A

A.1 HVAC Duct Systems Inspection GuideSecond Edition

A.1 VENTILATION AND AIR

CONDITIONING

Air is a gas that contains oxygen It envelops the planet

and fills all open spaces within buildings The

breath-ing function of human bebreath-ings removes oxygen from

air Thus, a replacement supply of oxygen is needed to

sustain life Oxygen is also used up in burning fuels

such as coal, oil, or gas to provide heat for human

com-fort Replacement of oxygenated air is needed for the

heating process as well

The process of providing a fresh supply of air for

hu-man need in buildings and comfort is called

ventila-tion Sometimes the removal of odorous or

contami-nated air is called ventilation as well Building codes

prescribe minimum amounts of ventilation

The process of treating air by filtering, cooling, and

adding or removing moisture from it is called air

con-ditioning

Motor driven fans move air from one space to another

(through ducts) to control it or to create desirable air

motion within occupied spaces Fans do this by

creat-ing enough pressure to overcome the resistance to flow

that naturally occurs when air molecules bump into

objects or have their direction changed

A.2 CENTRAL AIR HANDLING

SYSTEM

Central air handling systems are relatively large

net-works of air ducts that have fans located in an

equip-ment room somewhere in a building or on the roof of

the building Air ducts on the outlet side of the fan unit

are called supply air ducts They convey outdoor or

“treated” air to multiple rooms in selected zones

Zones may cover part of a floor or all of a floor They

may also cover parts of, or all of, several floors Supply

ducts operate with a positive pressure; that is, the

pres-sure in them is higher than the atmospheric prespres-sure in

the spaces they pass through

In a central supply-return system other ducts called

re-turn air ducts will collect air from the same rooms or

zones that the associated supply ducts serve and bring

it back to the heating, cooling, filtering, etc.,

appara-tus, for reconditioning before being sent back through

the supply fan The supply fan may serve both

func-tions (supply and return) or a separate return air will

mix with outdoor air in a fresh air intake plenum

lo-cated on the suction side of the supply limit

Alterna-tively, it may be exhausted to the outdoors The system

arrangement is diagrammed in Figure A-7 Several

forms of “central” systems can be used In some ofthem, not all of the return air is sent back to the centralstation fan unit Instead, it is returned to a satellite unitthat is located in its own zone where it is mixed withair coming from a central station unit and is then sentback to occupied spaces

Air handling systems may be of constant volume orvariable volume type These terms refer to the quantity

of air that is being circulated by the central station fanunit Varying the volume permits conserving energyspent in circulating and treating air since in many casesthe demand for heating or cooling varies over day-night and occupancy-use cycles

A.3 DEDICATED EXHAUST SYSTEMS

Air removal from toilet rooms, potentially nated areas of hospitals and laboratories, coolingrange areas, dishwashers, and boiler furnaces is nor-mally exhausted directly to the outdoors by systemsdedicated for the specific service The expense or diffi-culty of reconditioning air from such operations tomake it acceptable for occupant exposure is not con-sidered worthwhile In some cases, the thermal energy

contami-in exhaust air is saved by uscontami-ing heat recovery tus in the exhaust ducts In industrial plants, dedicatedexhaust systems collect and transport vapors, fumes,and particles that would cause health problems or in-terfere with work activity

appara-Another form of dedicated exhaust is smoke control.For a fire emergency, a separate smoke removal sys-tem can be activated or systems that would normally

be operating in return/recirculation mode can be verted to exhaust mode

con-The term “local exhaust” usually refers to air tion from a specific work operation site within a room.This contrasts with general exhaust which will apply

extrac-to area wide or an entire room

All exhaust systems require a source of replacement ormakeup air The source may be a supply system, cracks

or pores in the enclosure of exhausted space, opendoors or windows, undercut doors, or louvered ordampered openings Fan powered makeup air units arecommon in industrial facilities

A.4 ROOM AIR DISTRIBUTION

Air velocity level and the pattern of air movementfrom a supply point to an exhaust point in a room affectoccupant health, occupant comfort, and the efficiency

of temperature control Velocities under 15 feet perminute (fpm)(0.08 m/s) seem stagnant Those over 65

fpm (0.33 m/s) seem drafty The term “throw”

desig-nates the horizontal distance a supply air terminal

di-rects air before it reaches minimum velocity “Drop”

pertains to vertical fall before reaching low velocity

Air terminals that have volume dampers are called

reg-isters Special forms of supply terminals are called

dif-fusers

A.5 ROOM PRESSURE CONTROL

Rooms are designed to have positive pressure or

nega-tive pressure In general those that have more fan

pow-ered supply air than fan powpow-ered exhaust will have

positive pressure When the opposite situation exists,

the room will have negative pressure The intended

balance can be upset by unplanned opening of doors or

windows, the wrong position of dampers, failure of

in-teracting controls, unanticipated wind pressure on the

building exterior, and other circumstances Pressure

control is critical in a fire situation and in chemically

or biologically contaminated zones Normal and

emergency states of operation of fan systems must be

understood in order to preserve health and safety

A.6 INFILTRATION AND

EXFILTRATION

Infiltration is unintentional air leakage into buildings

Exfiltration is uncontrolled air leakage out of

build-ings These terms may also be applied to specific

compartments within buildings Typical rates of

leak-age for building components are given in the

ASH-RAE Fundamentals Handbook chapter on infiltration

and exfiltration The temperature, humidity, and

cleanliness of air from these sources can significantly

affect energy consumption costs as well as affect the

control of indoor environment for health and safetyreasons

A.7 CENTRAL ALARM CONTROL

STATIONS

Modern buildings often have central control/alarmstations that visually display and permit diagnosis ofthe operating condition of fire alarm, smoke detector,sprinkler, and air handling systems They also havestop-start controls that allow change of the operatingstate of the air handling systems The functions ofthese interdependent controls and systems are vital forthe safety of building occupants and they must be un-derstood by those responsible for verifying their con-dition

A.8 TESTING AND BALANCING

The operations of measuring and adjusting the

quanti-ty of air at fans, in ducts and at air terminals are nated “testing and balancing.” The shorthand term forthis is TAB Testing often involves measuring air pres-sures in ducts Static pressure is force exerted on a ductwall in a manner similar to that in an inflated balloon.Velocity pressure is a force acting in the direction offlowing air as in wind pressure The sum of static pres-sure and velocity pressure is called total pressure.Standard procedures for TAB are published by severalrespected organizations, including SMACNA

Standardized terminology and illustrations of ductsystem components are given in Figures A-1 andA-1M

A.3 HVAC Duct Systems Inspection GuideSecond Edition

THIS PAGE INTENTIONALLY LEFT BLANK

FIGURE A 1 SYMBOLS FOR HVAC SYSTEMS

20 x 12

S 30 x 12

BACK DRAFT DAMPER

GOOSENECK HOOD (COWL)

ACCESS DOOR (AD)

ACCESS PANEL (AP)

FOR SUPPLY & RETURN

IF APPLICABLE

OR F.O.B FLAT ON BOTTOM

NOTE F.O.T FLAT ON TOP

TRANSITIONS: GIVE SIZES.

INCLINED RISE (R) OR DROP

(D) ARROW IN DIRECTION OF

OR RETURN)

DUCT SECTION (EXHAUST

DUCT SECTION (SUPPLY)

SHOWN 2ND FIGURE, SIDE

DUCT (1ST FIGURE, SIDE

PRESSURE CLASS)

CONSTRUCTION (BY STATIC

POINT OF CHANGE IN DUCT

POWER OR GRAVITY ROOF VENTILATOR LOUVERED

VENTILATOR INTAKE (SRV) POWER OR GRAVITY ROOF

POWER OR GRAVITY ROOF VENTILATOR EXHAUST (CENTRIFUGAL FAN) PLAN UNIT HEATER (HORIZONTAL) UNIT HEATER (DOWNBLAST)

VENTILATING UNIT (TYPE AS SPECIFIED)

FAN & MOTOR WITH BELT GUARD & FLEXIBLE

COMBINATION DIFFUSER AND LIGHT FIXTURE

TERMINAL UNIT (GIVE TYPE AND OR SCHEDULE)

SUPPLY OUTLET CEILING, ROUND (TYPE AS SPECIFIED) INDICATE FLOW DIRECTION

CONNECTIONS SOUND TRAP DOOR GRILLE

EXHAUST OR RETURN AIR INLET CEILING (INDICATE

SUPPLY REGISTER (SR) (A GRILLE + INTEGRAL VOL.

RETURN (RG) OR EXHAUST (EG) GRILLE (NOTE AT FLR SUPPLY GRILLE (SG)

A.5 HVAC Duct Systems Inspection GuideSecond Edition

FIGURE A 1M SYMBOLS FOR HVAC SYSTEMS (METRIC)

S

762 x 305

S 762 x 305

MANUAL OPERATION

BACK DRAFT DAMPER

GOOSENECK HOOD (COWL)

ACCESS DOOR (AD)

ACCESS PANEL (AP)

AD AD MOD

VOLUME DAMPER

WYE JUNCTION

STANDARD BRANCH

FOR SUPPLY & RETURN

IF APPLICABLE

OR F.O.B FLAT ON BOTTOM

NOTE F.O.T FLAT ON TOP

TRANSITIONS: GIVE SIZES.

INCLINED RISE (R) OR DROP

(D) ARROW IN DIRECTION OF

AIR FLOW

OR RETURN)

DUCT SECTION (EXHAUST

DUCT SECTION (SUPPLY)

SHOWN 2ND FIGURE, SIDE

DUCT (1ST FIGURE, SIDE

PRESSURE CLASS)

CONSTRUCTION (BY STATIC

POINT OF CHANGE IN DUCT

POWER OR GRAVITY ROOF VENTILATOR LOUVERED

VENTILATOR INTAKE (SRV) POWER OR GRAVITY ROOF

POWER OR GRAVITY ROOF VENTILATOR EXHAUST

UNIT HEATER (CENTRIFUGAL FAN) PLAN UNIT HEATER (HORIZONTAL) UNIT HEATER (DOWNBLAST)

VENTILATING UNIT (TYPE AS SPECIFIED)

(ERV)

INLET CEILING (INDICATE

SUPPLY OUTLET CEILING, SQUARE (TYPE AS SPECIFIED) INDICATE FLOW DIRECTION

FAN & MOTOR WITH BELT GUARD & FLEXIBLE SOUND TRAP DOOR GRILLE

COMBINATION DIFFUSER AND LIGHT FIXTURE

TERMINAL UNIT (GIVE TYPE AND OR SCHEDULE)

SUPPLY OUTLET CEILING, ROUND (TYPE AS SPECIFIED) INDICATE FLOW DIRECTION TYPE)

EXHAUST OR RETURN AIR

SUPPLY REGISTER (SR) (A GRILLE + INTEGRAL VOL.

RETURN (RG) OR EXHAUST (EG) GRILLE (NOTE AT FLR SUPPLY GRILLE (SG)

CONTROL)

OR CLG)

305 x 152

ST DG

330 LPS

330 LPS

508 x 508

700 CFM 508

FIGURE A 2 SINGLE DUCT SYSTEM

POSSIBLE

OF VAV BOX (TYPICAL EACH COOLING COIL

RETURN AIR POSSIBLE

RETURN EXHAUST

RETURN AIR DAMPER

ADDITION

SPACE LOAD

FILTERS

AIR TERMINAL SUPPLY

FIGURE A 3 TERMINAL REHEAT SYSTEM

T

SUPPLY FAN AIR INTAKE

POSSIBLE PRE HEAT COIL

SPACE LOAD

RETURN AIR REGISTER

REHEAT COIL 1 REHEAT COIL 2

A.7 HVAC Duct Systems Inspection GuideSecond Edition

FIGURE A 4 MULTI ZONE SYSTEM

HEATING COIL (HOT DECK) DAMPERS

DAMPERS

COOLING COIL (COLD DECK)

MULTI ZONE UNIT

TO INDIVIDUAL COIL

ZONES

HEATING COIL

TERMINALS

RETURN AIR

ALTERNATE DESIGN

FIGURE A 6 DUCT SYSTEM EXAMPLE

H K

O

P Q

Y Z

½

* INDICATES DUCT LINER USED: SIZES ARE INTERIOR DIMENSIONS.

A.9 HVAC Duct Systems Inspection GuideSecond Edition

FIGURE A 6M DUCT SYSTEM EXAMPLE (METRIC)

PLENUMS Y

VD VD

* INDICATES DUCT LINER USED: SIZES ARE INTERIOR DIMENSIONS.

SAMPLE SITUATION WITH A TERMINAL REQUIRING 0.15 in wg (37 Pa) STATIC, A BRANCHDAMPER REQUIRING 0.15 in wg (37 Pa) STATIC, DUCT DESIGNED FOR 0.1 in wg

LOSS/100 ft (25 Pa/30 m) AND FITTING LOSSES EQUAL TO STRAIGHT DUCT LOSS THECIRCUIT CAN BE 100 L.F (30 m) LONG BEFORE½in wg (125 Pa) LOSS IS EXCEEDED

FIGURE A 7 DUCT PRESSURE CLASS DESIGNATION

ST C

AIR HDLG UNIT EXTERNAL STATIC IS 1.5 in

wg (375 Pa) FAN STATIC IS 3 in wg (750 Pa)

LOUVER

0.7 in wg (174 Pa) STATIC

1.5 in wg (375 Pa) STATIC

(375 Pa) STATIC

¾ in P.D.

(187 Pa) SOUND TRAP

(187 Pa) STATIC

ELIM

THE NUMBER ASSIGNS PRESSURE CLASS WHICH WILL

ACCOMMODATE MAXIMUM OPERATING PRESSURE IN

THE DUCT SUBSECTION THE SYMBOL CONTINUES THE

ASSIGNMENT UNTIL THE DUCT TERMINATES OR

ANOTHER SYMBOL APPEARS

“N” SUPERSCRIPT ISUSED TO CLARIFYNEGATIVE PRESSUREDUCT ON CERTAIN LESSOBVIOUS APPLICATIONS

VARIABLE VOLUME UNITS, MIXING BOXES,ETC REQUIRE A MINIMUM OPERATINGPRESSURE, BUT THE DUCT SHOULD BEASSIGNED A CLASS FOR THE MAXIMUMOPERATING PRESSURE THAT MAY OCCUR

TERMINAL UNIT (BOX)

MEANS 1 in wg (250 Pa)

CLASS SEE SMACNA HVAC DCS

(Second Edition, 1995) TABLE 1 1

APPENDIX B

DUCT CONSTRUCTION MATERIALS

DUCT CONSTRUCTION MATERIALS APPENDIX B

Materials used for rigid ducts include: galvanized

steel, black carbon steel, aluminum, stainless steel,

copper, fiberglass reinforced plastic (FRP), polyvinyl

chloride (PVC), polyvinyl steel (PVS), concrete,

fi-brous glass (duct board), and gypsum board Codes,

construction standards, and the design documents

gov-erning air handling systems define acceptable limits of

use of each material This Appendix contains a brief

review of materials application

B.1 GALVANIZED STEEL

APPLICATIONS—Widely used as a duct material for

most air handling systems; not recommended for

cor-rosive product handling or temperatures above 400°F

(204°C)

ADVANTAGES—High strength, rigidity, durability,

rust resistance, availability, non-porous, workability,

and weldability

REMARKS—Galvanized steel sheet is customarily

available in commercial and lock forming quality See

additional characteristics in Table B-1

B.2 CARBON STEEL (BLACK IRON)

APPLICATIONS—Breechings, flues, stacks, hoods,

other high temperature duct systems, kitchen exhaust

systems, ducts requiring paint, or special coating

ADVANTAGES—High strength, rigidity, durability,

availability, paintability, weldability, non-porous

REMARKS—Hot-rolled sheet is manufactured by

hot-rolling slabs in a continuous mill Cold-rolled

sheet is manufactured from hot-rolled, descaled coils

by cold reducing to the desired thickness, generally

followed by annealing Hot-rolled carbon steel is

gen-erally softer, less precisely rolled, less expensive, and

is used more frequently than cold-rolled steel See the

specifications in Table B-2

B.3 STAINLESS STEEL

APPLICATIONS—Duct systems for kitchen exhaust,

moisture laden air, fume exhaust

ADVANTAGES—High resistance to corrosion from

moisture and most chemicals, ability to take a high

polish

REMARKS—Available in many different alloy binations Types 304 and 316 are most commonlyused Stainless is usually available in the finishes listed

com-in Table B-3

APPLICATIONS—Duct systems for moisture ladenair, louvers, special exhaust systems, ornamental ductsystems

ADVANTAGES—Light weight, resistance to ture, corrosion (salt free), availability

mois-REMARKS—Various alloys are available in sheetform with the 3000-H14 temper series being the mostcommonly specified for duct systems A “utilitygrade” sheet is also available Sheets can also be ob-tained with embossed or anodized surfaces The com-monly used grade has about one half of the tensilestrength and one third of the rigidity of steel It also has

high thermal expansion See additional characteristics

in Table B-4

APPLICATIONS—Duct systems for exposure to side elements and moisture laden air, certain chemicalexhaust, ornamental ductwork, hoods

out-ADVANTAGES—Accepts solder readily, durable, sists corrosion, non-magnetic

re-REMARKS—Its connection to other metals can result

in galvanic corrosion Its use is limited to pressure low 2 in wg (500 Pa)

be-B.6 FIBERGLASS REINFORCED

PLASTIC (FRP)

APPLICATIONS—Chemical fume exhaust, bers, underground duct systems

scrub-ADVANTAGES—Resistance to corrosion, strength

REMARKS—Codes usually limit its application though NFPA Standard 91 covers FRP, provisionstherein relate more to pipe than to duct

Al-B.2 HVAC Duct Systems Inspection GuideSecond Edition

B.7 POLYVINYL CHLORIDE (PVC)

APPLICATIONS—Exhaust systems for chemical

fumes and hospitals, underground duct systems

ADVANTAGES—Resistance to corrosion, weight,

weldability, ease of modification

REMARKS—Use is restricted by codes and its

com-bustibility and toxicity ratings

B.8 POLYVINYL STEEL (PVS)

APPLICATIONS—Underground duct systems,

mois-ture laden air, and corrosive air systems

ADVANTAGES—Resistance to corrosion, availability

REMARKS—Polyvinyl steel is a polyvinyl chloride

plastic coating heat-fused to galvanized steel 2 mil

(0.05 mm) and 4 mil (0.10 mm) coating thicknesses

usually are standard, with steel gages (US standard)

available from 26 ga (0.55 mm) through, and

includ-ing, 14 ga (2.0 mm) This product is most popular in

spiral seam pipe and is available in flat sheets and coil

stock of lockforming quality It is susceptible to

coat-ing damage and temperature limits

REMARKS—Due to high smoke generation rating,

sprinklers may also be required by codes

APPLICATIONS—Underground ducts, air shafts

ADVANTAGES—Compression strength, corrosion

resistance

B.10 ASBESTOS CEMENT

APPLICATIONS (FORMER)—Underground ductsystems, kitchen exhaust, chemical exhaust, high tem-perature duct systems, flues, and vents

ADVANTAGES—Resistance to most chemicals, can

be used up to 2000°F (1093°C)

REMARKS—Asbestos products are now subject tomany government regulations

B.11 RIGID FIBROUS GLASS

APPLICATIONS—Interior HVAC low pressure ductsystems

ADVANTAGES—Lightweight, thermal insulationand vapor barrier, acoustical qualities, ease of modifi-cation, inexpensive tooling for fabrication

REMARKS—Construction standards and code lated provisions must be strictly followed

Thickness in Inches Weight Thickness in Millimeters

b Tolerances are valid for 48 in (1220 mm) and 60 in (1524 mm) wide coil and cut length stock - other dimensionsapply to other sheet widths and to strip

c The lock forming grade of steel will conform to ASTM A653 (formerly ASTM A527)

d The steel producing industry recommends that steel be ordered by decimal thickness only Thickness and zinc ing class can be stenciled on the sheet The gage designation is retained for residual familiarity reference only

coat-e Minimum weight in this table is based on the following computation:

Min sheet thickness (t) minus 0.001 in of G60 coating times 40.8 lb per sf per inch plus 0.0369 lb per sf of zinc.G90 stock would be comparably calculated from:

minimum weight = (t - 0.00153 in.) 40.8 + 0.0564.

However, scale weight may run 2% (or more) greater than theoretical weight Actual weight may be near 40.82 lbper sf per inch

f G60 coating, per ASTM A653 and ASTM A90, has 0.60 oz/sf (triple spot test) total for two sides 0.59 oz/sf of zincequals 0.001 in 1 oz is 0.0017 in and is 305.15 g/m2 G90 coating is 0.90 oz/sf (triple spot test), or 0.00153 in.Magnetic gage measurement of zinc coating may have 15% error

g ASTM A2092, Practices for Preparation of Zinc-Coated Galvanized Steel Surfaces for Paint, includes mill phosphatizing

h ASTM A755 is the Specification for Sheet Steel, Metallic Coated by the Hot-Dip Process and Prepainted by theCoil-Coating Process for Exterior Building Products Other information is available from the National Coil CoatersAssociation, Philadelphia, PA

i Much chemical and atmospheric corrosion information is available from ASM International in Metals Park, Ohioand from NACE International in Houston, TX

j A principle international standard is ISO 3575, Continuous Hot-Dip Process, Zinc-Coated Carbon Steel Sheet ofCommercial, Lock Forming, and Drawing Qualities

B.4 HVAC Duct Systems Inspection Guide • Second Edition

Preferred inM.S

Gage

Weight

lb/sf(kg/m2) Nominal

in (mm)

Preferred inThicknessMillimeters

a Manufacturers Standard Gage is based on a theoretical steel density of 489.6 lb/cf, or 40.80 lb/sf per inch

of thickness plus 2.5% normally experienced increase in delivery weight Thus, the weight basis associatedwith thickness specifications is 41.82 lb/sf per inch

b U.S Standard Gage, the legal gage since 1893, although based on the density of wrought iron 480 lb/cf, used 40.00lb/sf/in for both iron and steel Thus, U.S gage thicknesses are derived from weights 2% lighter than steel

c The table is based on 48 in (1220 mm) width coil and sheet stock 60 in (1524 mm) stock has the same tolerĆance for gages listed except for 16 gage which has ± 0.007 in in hot-rolled sheet

d See ASTM Standards A366 (cold-rolled order form), A568 (properties of hot-rolled and cold-rolled sheet ofcommercial quality), and A569 (hot-rolled order form)

e Thickness and weight in customary units are based on data in the AISI Carbon Sheet Steel Products Manual.Metric conversions listed here are straight multiplications for comparison purposes Individual manufacturĆers may quote other tolerances

f ANSI is the American National Standards Institute Standards B32.3 actually covers a wider range of thickĆness than listed here